This invention relates to method and apparatus for applying and evenly coating a moving web of material with a predetermined amount of a liquid and characterized by simplicity of design of the apparatus, uniformity of application of the liquid and accurate control of the amount of liquid applied.
In many manufacturing operations, it is necessary to treat a continuous web or sheet of material with a liquid for various purposes in the manufacturing operation. In this type of manufacturing operation, roll coating processes are among the most frequently used and involve the use of a kiss roll principal with a hard roll rotating in a bath of coating liquid and in contact with one surface of the web or sheet of material to be coated for applying the coating liquid to the surface of the web or sheet of material. The amount of liquid coated onto the web of material in this roll coating or kiss roll process is controlled by a doctor blade or other pick-up devices contacting the surface of the roll. These methods and apparatuses produce difficulty in controlling the amount of coating liquid applied to the web of material and obtaining a uniform coating on the web of material.
The above problems are particularly acute when the web or sheet of material being coated is of a relatively unflexible or stiff construction and the material of the web or sheet is very absorbent. With non-flexible or stiff material, the web or sheet will not evenly contact the hard kiss roll utilized in conventional roll coating processes and, therefore, a spotty or non-uniform application of the coating liquid will result. Also, with a very absorbent material, a uniform application of the coating liquid by a hard kiss roll is difficult to obtain since the coating liquid is not usually uniformly distributed along the hard kiss roll and the absorbent material will quickly absorb the coating liquid without allowing the coating liquid to be spread out or evenly distributed on the surface of the web of material.